A: Investors who could have predicted the future would be very rich right now.

Hindsight is certainly crystal clear with investing. The biggest gains in investing often go to investors who bet on the improbable events that wind up happening and turning extremely profitable. The past few years have certainly been a dramatic example.

All told, an investor who would have picked the best stock in the current Standard & Poor's 1500 index since 2010 would have been an astounding 13,791% gain. An initial $10,000 invested at the start of 2010 would be worth $1.4 million in July 2013.

Getting that return would have taken incredible luck, though. The best stock in 2010 was semiconductor company Entropic Communications with a 293.5% gain. And then in 2011, the best gainer was biotech Questcor Pharmaceuticals at 182.3%. The winner in 2012 was building products maker Headwaters at 285.6%. And so far this year, through July 31, the best stock has been food distributor Supervalu with a 224.3% gain.

Looking back at the winning stocks in the past doesn't give a realistic return expectation. But it can show investors, historically, how profitable uncanny luck can be. Investors cannot possibly expect to enjoy this kind of amazing return, and looking back historically distorts how hard it would have been. But still, the exercise shows the power of the stock market.